1. Field of the Invention
The present invention relates generally to a spin transfer torque magnetic random access memory (STTMRAM) element, and, more particularly, to an STTMRAM element having a laminated synthetic graded free layer.
2. Description of the Prior Art
Spin transfer torque magnetic random access memory (STTMRAM) is one of the next generations of non-volatile memory currently under development. In STTMRAM, writing magnetic bits is achieved by using a spin polarized current through the magnetic tunnel junction (MTJ), instead of using a magnetic field. The STTMRAM write current scales down with smaller MTJ size in future technology nodes. STTMRAM has significant advantages over the recently-commercialized magnetic-field-switched MRAM, making it a viable candidate for replacing MRAM.
However, one of problems currently preventing use of STTMRAMs is reliable storage of data, which occurs by the free layer thereof switching magnetic orientation to save a logic state of ‘1’ or ‘0’. Thermal stability plays a strong role in affecting switching of the free layer in that the higher thermal stability, the more reliable the switching of the free layer. Otherwise, STTMRAM offers fast read/write speed and has lower voltage requirement and as such is believed to be an ideal candidate for replacing SRAM as an embedded memory, among other foreseeable applications.
An example of a prior art STTMRAM element 1 is shown in FIG. 1. The element 1 is shown to include an underlayer 2 on top of which is shown formed an antiferromagnetic layer 3, on top of which is shown formed a magnetic layer 4, on top of which is shown formed an AF coupling layer 5, on top of which is shown formed a magnetic layer 6, on top of which is shown formed a barrier layer 7, on top of which is shown formed a magnetic layer 8, on top of which is shown formed a capping layer 9. The element 1, as do other prior art STTMRAM elements, suffers from low thermal stability, which adversely affects the switching behavior thereof.
What is needed is a STTMRAM element with improved thermal stability while maintaining ease of switching the magnetization state thereof with an electrical current.